Laser Communication Research Articles

Response time of the type-II superlattice InAs/InAsSb mid-infrared interband cascade photodetector for HOT conditions

The article presents III-V InAs/InAsSb type-II superlattice (T2SL) mid-wave infrared (MWIR, 100 % cut-off wavelength, λcut-off ∼ 7.5 μm at 333 K) interband cascade photodetector (ICIP) developed to operate at temperatures > 300 K. That device solves the low quantum efficiency (QE) problem of the typical “thick absorber” photodetectors designed for high operating temperature (HOT, > 300 K) conditions. The 5-stage epilayer was grown by molecular beam epitaxy (MBE) on the lattice-mismatched GaAs substrates where absorbers are connected by the highly doped standard n+/p+ tunnel junctions. The developed and analyzed high-speed MWIR devices should be implemented in the emerging fields such as frequency comb spectroscopy (FCS), free space optical communication (FSO) and light detection and ranging (LIDAR). The majority of the MWIR ICIPs’ research have been focused on the QE increase and dark current suppressing to improve the detectivity (D*) while the high- frequency operation (HFO) is still not completely investigated. We report on the MWIR InAs/InAsSb T2SLs ICIP where tradeoff between response time and detectivity was obtained. The time constant being limited by the carriers’ transit time reaches ∼ 16 ns corresponding to 3-dB bandwidth, f3-dB ∼ 10 MHz (detectivity ∼ 2 × 108 cmHz1/2/W without immersion GaAs lens with ∼ 0.53 μm single absorber) for λcut-off ∼ 7.5 μm at 333 K and unbiased conditions. Under 1 V time constant reaches ∼ 2.4 ns (f3-dB ∼ 66 MHz).

Radially polarized partially coherent beams with prescribed sinh-Gauss non-uniform correlation structure

We introduce a kind of radially polarized partially coherent beam with a prescribed sinh-Gauss non-uniform correlation structure, named a radially polarized sinh-Gauss non-uniformly correlated (RPSNC) beam. Utilizing the ordinary Huygens–Fresnel principle, we derive the analytical formulas for the spectral intensity and the spectral degree of polarization (DOP) in free space and investigate the beam’s propagation properties through numerical simulations. The results demonstrate that RPSNC beams exhibit a self-focusing property during propagation, with the focal position adjustable by varying the coherence length. Additionally, the spectral DOP in the central region forms a distinctive single-ring structure as the beam propagates. These unique properties make RPSNC beams promising for applications in free-space optical communications, beam shaping, and optical trapping.

Deep learning-based prediction of atmospheric turbulence towards satellite-to-ground laser communication

Deep learning-based prediction of atmospheric turbulence towards satellite-to-ground laser communication

Retraction Note: Performance analysis of high-speed integrated OAM-OCDMA transmission in FSO communication link: Impact of weather attenuation

Retraction Note: Performance analysis of high-speed integrated OAM-OCDMA transmission in FSO communication link: Impact of weather attenuation

Hollow MoS2-Co3S4 heterostructures derived from ZIF-67 as saturable absorber for generating gigahertz repetition frequency mode-locked fiber lasers

In practical applications, high repetition frequency (HRF) lasers are widely used in the fields of material processing, laser communication and medical therapy. In this work, the passive harmonic mode-locked (HML) technique is used to realize a HRF fiber laser in GHz level, effectively overcoming the limitations of traditional fiber laser structures. In order to maximize the advantages of nanomaterials, we synthesized high-purity hollow MoS2-Co3S4 heterojunction materials by hydrothermal method. Then, a “sandwich” structure saturable absorber (SA) was prepared by photodeposition, and its nonlinear optical properties were investigated. The results demonstrate that the modulation depth and saturation intensity of MoS2-Co3S4 SA are 24 % and 4.53 MW/cm2, respectively. The fiber laser based on MoS2-Co3S4 SA could realize the fundamental frequency mode-locked at 23.11 MHz with a pulse width of 0.99 ps. In addition, various high-order HML are realized with this laser system capable of stable operation for extended periods up to the highest repetition frequency of 1.109 GHz achieved thus far in this field. This research provides strong support to promote the development and commercialization of HRF fiber lasers.

Simultaneous Vibration and Temperature Real-Time Monitoring Using Single Fiber Bragg Grating and Free Space Optics

Simultaneous monitoring of temperature and vibration of electromechanical systems, public buildings, and volcanic terrain is an important indicator of preventing accidents. This work showcases the simultaneous temperature and vibration measurement using a single-fiber Bragg grating (FBG) sensor. The concurrent interrogation of vibration and temperature by the FBG sensing system can be integrated with free space optics (FSO), which saves on the costs associated with fiber optic cables and overcomes terrain barriers. Furthermore, the real-time measured vibration frequencies and different temperature levels can be recognized by a deep neural network (DNN) sequential model. In addition to the FSO support, the sensing system can be arranged in multiple sensing locations to form a wide range of measurements, offering a highly cost-effective solution.

Misalignment tolerance enhancement of vector beams in free-space optical communication link

Misalignment tolerance enhancement of vector beams in free-space optical communication link

Three-wavelengths integrated SiN optical phased array for LiDAR and FSO data link applications

We propose a scalable integrated silicon nitride optical phased array (OPA) enabling multi-beam emission and two-dimensional continuous beam steering for light detection and ranging (LiDAR), free-space optics (FSO), and data link applications. The emitters are optimized grating couplers for wavelengths of 800 nm, 850 nm, and 905 nm. We propose three OPAs, two with 8 emitters and one with 16 emitters. The OPAs are characterized at a wavelength of 850nm. The measured beam size of the OPAs are 0.96° ×0.12°, 0.69° ×5.42°, and 0.7° ×1.53°. A lateral beam steering of ±12.35° is measured. The proposed configuration of the thermo-optical phase shifters along the OPA tree provides a simple multi-level beam splitting resolution for each OPA. By enhancing the unwanted side lobes, a discrete angular selection resolution is achieved, improving from 6.1° to 0.082°. We proposed an array of heaters to suppress the unwanted side lobes of the radiation pattern, and its performance is measured and presented. We measured the modulated beam considering pulses with different duty cycles up to 5 MHz and data rates up to 6.25 Mb/s.

An 80 Gbps Integrated PDM‐OAM‐Enabled‐FSO Transmission for Implementing 5G Services Under Riyadh Weather Conditions

ABSTRACTThe surge in demand of high‐capacity wireless information transmission links has led to emergence of novel multiplexing techniques for free space optics (FSO) over the past few years. Two such important techniques are polarization division multiplexing (PDM) and orbital angular momentum (OAM) multiplexing. This article investigates the integration of PDM and OAM techniques in a FSO transmission system to enable 5G communication services in Riyadh City, Saudi Arabia. Four OAM beams () of 2‐polarization states of a single frequency laser beam are used to transport 10 Gbps data independently. A total of 80 Gbps net transmission rate is achieved. The visibility data for Riyadh city are collected from Saudi Meteorological Department and the attenuation coefficient is calculated using Kim, Kruse, and Al‐Naboulsi attenuation models. The performance of all the PDM‐OAM modulated signals is compared for the three‐attenuation models in terms of bit error rate, eye diagrams, and Q Factor of the signal at the receiver. The results show that using Kim and Kruse models, with attenuation of 0.62 and 0.64 dB/km, the maximum range of 3.8 km is achieved. This is, however, reduced to 2.4 km using Al‐Naboulsi model having attenuation of 2.03 dB/km with acceptable limits of Q Factor (∼6 dB) and BER (∼9).

Relay aided UWOC-SMF-FSO based hybrid link for underwater wireless optical sensor network

The Internet of Underwater Things (IoUTs) connects underwater devices to communicate, sense surroundings, and transmit data. Acoustic communication faces bandwidth limitations, making underwater wireless optical communication-free space optics (UWOC-FSO) hybrid systems a promising alternative. However, maintaining sufficient power budget and signal-to-noise ratio (SNR) is a challenging task, making wavelength translation (WT) from visible to infrared (IR) at the water-fiber-air interface crucial for reliable signal transmission. In this paper, we propose an underwater wireless optical communication-single mode fiber-free space optics (UWOC-SMF-FSO) hybrid link based on a photo-detection, remodulate, and forwarding (PRF) relay and intensity modulation-direct detection (IM/DD) scheme for 8 × 1-Gb/s underwater optical wireless sensor network (UWOSN). The PRF relay is installed at a remotely operated underwater vehicle (ROV) to perform WT from visible range to IR. The performance of the sensors is analyzed for different water bodies and weather conditions of underwater and free space optics channels, respectively using metrics of Bit-error rate (BER) and Quality factor (Q-factor) employing Gamma–Gamma channel model. The simulation results show that forward-error correction (FEC) target BER of 10−4 for sensors is achieved under different water bodies and weather conditions. The results obtained from this study show that the proposed UWOC-SMF-FSO hybrid link is flexible, resilient to adverse channel effects, and can be a potential candidate for implementation of high-speed long-distance future IoUTs.

Demonstration of daytime CubeSat-to-ground laser communication in OOK modulation with a dual-mode superconducting nanowire single-photon detector

Demonstration of daytime CubeSat-to-ground laser communication in OOK modulation with a dual-mode superconducting nanowire single-photon detector

Refined Metamodel Disturbance Observer-Based Control for Coarse Pointing Assembly Under Constraints

The target tracking performance of the coarse pointing assembly (CPA) is a critical factor in determining the data transmission efficiency of the inter-satellite laser communication. However, under the influence of multiple disturbances, such as gimbal coupling torque, friction, and satellite-transmitted vibration, the angle tracking performance of the CPA can be decreased, which then affects the safety of the system in terms of angular velocity. To address the performance and safety requirements of the CPA, this paper proposes a refined metamodel disturbance observer-based state constraints controller. First, a refined metamodel disturbance observer is proposed to achieve accurate disturbance estimation by combining the data-driven state-space Kriging metamodeling method with a refined disturbance observer. Both disturbance numerical data and partially known information (e.g. vibration frequency and structure) are fully utilized to reduce estimation conservatism. Second, based on the observer, a state constraint controller is designed to ensure the angle tracking performance and angular velocity constraints. Finally, the effectiveness and robustness of the proposed control method are validated through numerical simulations, indicating an enhanced angle tracking performance compared to the traditional disturbance observer-based control method.

Single laser based novel wavelength shift keying scheme for ground to satellite bidirectional links

Abstract Laser communication in space is gaining more recognition due to its ability to provide a much broader and unregulated data transmission capacity compared to traditional radio frequency systems, while also significantly decreasing the size, power requirements, and weight of the communication system. In this work, a novel technique for the generation of a wavelength shift keying (WSK) signal for the bidirectional transmission of 10 Gbps data between the ground station and low Earth orbit (LEO) satellite is presented. Our proposed scheme requires a single laser source to transmit WSK signal, that generally requires two wavelength sources to transmit the binary data bits. Furthermore, the scheme allows us to remodulate the optical signal received at the LEO satellite for downlink signal transmission. Therefore, the requirement of a laser source at the LEO satellite is eliminated, achieving the much desirable goals of low power consumption, weight and cost. The free space optical (FSO) channel is modelled using the gamma-gamma channel model. The performance of the proposed link is also compared with a conventional On-Off keying (OOK) based modulation scheme by using bit-error-rate (BER) as the performance metric.

High-Performance Telescope System Design for Space-Based Gravitational Waves Detection.

Space-based gravitational wave (GW) detection employs the Michelson interferometry principle to construct ultra-long baseline laser interferometers in space for detecting GW signals with a frequency band of 10-4-1 Hz. The spaceborne telescope, as a core component directly integrated into the laser link, comes in various configurations, with the off-axis four-mirror design being the most prevalent. In this paper, we present a high-performance design based on this configuration, which exhibits a stable structure, ultra-low wavefront aberration, and high-level stray light suppression capabilities, effectively eliminating background noise. Also, a scientifically justified positioning of the entrance and exit pupils has been implemented, thereby paving adequate spatial provision for the integration of subsequent optical systems. The final design realizes a wavefront error of less than λ/500 in the science field of view, and after tolerance allocation and Monte Carlo analysis, a wavefront error of less than λ/30 can be achieved with a probability of 92%. The chief ray spot diagram dimensions are significantly small, indicating excellent control of pupil aberrations. Additionally, the tilt-to-length (TTL) noise and stray light meet the stringent requirements for space-based gravitational wave detection. The refined design presented in this paper proves to be a more fitting candidate for GW detection projects, offering more accurate and rational guidance.

Selection of OAM signal constellations for atmospheric channels using optimal transport theory

We describe a method for determining optimal selections of orbital angular momentum (OAM) superpositions for OAM signal modulation in free-space optical communications using a measure of distance in the context of the Optimal Transport theory. Within the range of topological charges ℓ = −20 to ℓ = 20 we design OAM constellations using 16 to 128 symbols consisting of solos, duets, trios, and quartets of OAM modes. We propose a classification strategy requiring relatively low complexity to evaluate the performance of these constellations, achieving a classification error smaller than 1/1000 in weak to strong turbulence conditions for the 16-OAM constellation. We have found that the optimal set shows some dependence on the receiver’s architecture, so we offer results for optical detectors based on the conjugate projection, the mode sorter, and the Shack-Hartmann sensor.

Mid-infrared 2D nonredundant optical phased array of mirror emitters in an InGaAs/InP platform

The extension of photonic technologies such as lidar and free-space optical communications from the traditional visible and near-infrared wavelengths to longer wavelengths can improve performance in adverse environments such as haze, fog, smoke, or strong solar background. Non-mechanical beam steerers will be a critical component of the low size, weight, and power modules needed for the portable or unmanned systems deployed in these environments. In this work, we demonstrate the first 2D optical phased array for non-mechanical beam steering in the mid-infrared spectral region. We combine a total-internal-reflection mirror emitter with a nonredundant array of 30 elements to carry out 2D beam steering at a single wavelength of 4.6 µm. The experiment yielded ∼600 resolvable far-field points, with ∼2400 points over a 28° × 28° field of view calculated theoretically. Moreover, the device was fabricated in a passive InGaAs/InP platform, contributing another advance in the ongoing development of quantum cascade laser-based photonic integration.

Design Considerations for Wavefront Sensing with Self-referencing Interferometers in Adaptive Optics Systems

In this work, we show the design and implementation of wavefront sensing with a self-referencing interferometer (SRI). The SRI is developed to aid adaptive optics (AO) control, via deformable mirrors, in correcting wavefront error from atmospheric turbulence in free-space optical (laser-based) communication links. The SRI is used here given its potential to outperform more common wavefront sensors in functioning over weak through strong turbulence conditions. In this study, we identify and analyse the key parameters in the SRI's optical design and show guiding principles for its subsequent image processing.

780 nm Narrow Linewidth External Cavity Diode Laser for Quantum Sensing.

To meet the demands of laser communication, quantum precision measurement, cold atom technology, and other fields for narrow linewidth and low-noise light sources, an external cavity diode laser (ECDL) operating in the wavelength range around 780 nm was set up with a Fabry-Pérot etalon (F-P) and an interference filter (IF) in the experiment. The interference filter type ECDL (IF-ECDL) with butterfly-style packaging configuration has continuous wavelength tuning within a specified range through precise temperature and current control and has excellent single-mode characteristics. Experimental results indicate that the output power of the IF-ECDL is 14 mW, with a side-mode suppression ratio (SMSR) of 54 dB, a temperature-controlled mode-hop-free tuning range of 527 GHz (1.068 nm), and an output linewidth of 570 Hz. Compared to traditional lasers operating at 780 nm, the IF-ECDL exhibits narrower linewidth, lower noise, and higher spectral purity, and its dimensions are merely 25 × 15 × 8.5 mm3 weighing only 19.8 g, showcasing remarkable miniaturization and lightweight advantages over similar products in current research fields.

Simultaneous bi-directional all-optical multipoint-to-multipoint switching for free-space optical communication networks

A new, to our knowledge, simultaneous bi-directional all-optical multipoint-to-multipoint switching scheme is proposed and experimentally demonstrated for free-space optical (FSO) communication networks. Through tuning the optical switch at the core node, the communication link between each two arbitrary remote nodes can be established. The multipoint transmission performance is tested in a turbulence-tunable atmospheric cell using a 6.25 Gbit/s quadrature phase-shift keying (QPSK) signal. At the bit error rate (BER) of 1×10−3, the power penalty is <3.5dB with a 250°C temperature difference of the atmospheric cell. Moreover, this scheme is compatible with all-optical wavelength conversion, which can achieve strict transparency for different modulation formats. Our proposed scheme offers the possibility to provide an efficient, low-cost, and high-speed method for simultaneous bi-directional all-optical multipoint-to-multipoint FSO communications.

Enhancing Long-Term Robustness of Inter-Space Laser Links in Space Gravitational Wave Detection: An Adaptive Weight Optimization Method for Multi-Attitude Sensors Data Fusion

The stable and high-precision acquisition of attitude data is crucial for sustaining the long-term robustness of laser links to detect gravitational waves in space. We introduce an effective method that utilizes an adaptive weight optimization approach for the fusion of attitude data obtained from charge-coupled device (CCD) spot-positioning-based attitude measurements, differential power sensing (DPS), and differential wavefront sensing (DWS). This approach aims to obtain more robust and lower-noise-level attitude data. A system is designed based on the Michelson interferometer for link simulations; validation experiments are also conducted. The experimental results demonstrate that the fused data exhibit higher robustness. Even in the case of a single sensor failure, valid attitude data can still be obtained. Additionally, the fused data have lower noise levels, with root mean square errors of 9.5%, 37.4%, and 93.4% for the single CCD, DPS, and DWS noise errors, respectively.